Tests if a string has a permissible name for a term constant.
DESCRIPTION
When applied to a string, allowed_term_constant returns true if
the string is a permissible constant name for a term, that is, if it
is an identifier (see the DESCRIPTION for more details), and false
otherwise.
FAILURE
Never fails.
EXAMPLE
The following gives a sample of some allowed and disallowed constant
names:
- map Lexis.allowed_term_constant ["pi", "@", "a name", "+++++", "10"];
> val it = [true, true, false, true, false] : bool list
COMMENTS
Note that this function only performs a lexical test; it does not
check whether there is already a constant of that name in the current
theory.